1. Field
The present invention relates to a refrigerator, and more particularly, to a refrigerator which can stably keep beverages in a supercooled state and a method to control the same.
2. Description of the Related Art
A refrigerator is generally a device that supplies cool air generated by a cooling unit to a storage compartment to maintain the freshness of various foods for a long time. If the inner temperature of the storage compartment of the refrigerator is controlled appropriately, it is possible to keep beverages in a supercooled state. By keeping beverages in the supercooled state, users can obtain beverages that are neither completely frozen nor completely melted, referred to as “slush”.
When the temperature of a beverage is reduced below the freezing point at 1 atmosphere, its phase generally changes from liquid to solid but, in some cases, it may be in a supercooled state without being changed to solid. The state of liquid in a supercooled state without freezing below the freezing point is thermodynamically referred to as a metastable state. In the metastable state, the supercooled liquid is neither completely unstable nor completely stable so that it instantly undergoes a phase change to solid upon receiving disturbance, such as impact or vibration from ambient environments. Thus, the user can obtain slush from a beverage by cooling the beverage below the freezing point in a refrigerator without allowing any disturbance to be applied, and then removing the beverage from the refrigerator and applying disturbance at a desired time.
To keep a beverage in a refrigerator in a supercooled state, it is necessary to cool the beverage below the freezing point. The supercooled level of the beverage increases as the inner temperature of the refrigerator decreases. However, if the inner temperature is too low, the supercooled state is broken to allow the beverage to freeze, thereby failing to obtain slush. The limit of the supercool temperature of commercial beverages generally ranges from about −8° C. to about −12° C., although this value varies slightly depending on the type of beverage. Thus, it is possible to keep beverages in a supercooled state by adjusting the refrigerator temperature in a range of temperatures slightly higher than the supercool temperature limit.
An example of a cooling device which can supercool beverages is described in Japanese Patent Application Publication No. 2003-214753 (entitled “COOLING DEVICE TO SUPERCOOL BEVERAGE” and published on Jun. 30, 2003). The cooling device of this publication supplies appropriate cool air to a storage compartment, in which beverages are stored, to keep the temperature of the storage compartment below the freezing point.
However, the conventional cooling device collectively adjusts the inner temperature of the refrigerator regardless of the types of beverages so that beverages with a relatively high freezing point may freeze while the supercooled level of beverages with a relatively low freezing point may be reduced.
Further, the probability that the beverages will freeze near the lowest temperature point is increased if the adjusted inner temperature of the refrigerator greatly varies. Thus, the inner temperature of the refrigerator must be adjusted with a variation less than a specific temperature level (for example, ±0.5° C.). However, it is very difficult to satisfy this requirement through the method of supplying cool air using the conventional cooling device.